This invention relates to the art of electrochemical cells, and more particularly to a new and improved alkali metal cell having end of life indication.
Electrochemical cells having high energy density and current delivery capability have been developed for use with implantable medical devices. In particular, alkali metal/solid cathode and alkali metal/oxyhalide cells have been developed wherein the anode typically is lithium and the electrolyte is either solid or liquid. In addition, it has been found to be advantageous to provide a casing of conductive material in operative contact with either the anode or cathode to provide, respectively, a case negative or case positive configuration.
When electrochemical cells are used with implantable medical devices, it is important to provide a warning indication toward the end of discharge of the cell signalling an approaching end-of-life of the cell so that appropriate measures can be taken for cell replacement. Typically this is accomplished by a detectable step or transition occurring in the output voltage of the cell which serves as an indication of cell end-of-life. In the design of such an electrochemical cell it would be highly desirable to provide a relatively larger interval between the onset of end-of-life of the cell and the time when replacement of the cell is needed.